1. Field of the Invention
The present invention relates to a heat-shrinkable polyester film having excellent crystallinity, which can overcome the problems according to pre-crystallization occurring at a neopentyl glycol content larger than 25 mol %, the product and process problems caused by thermal decomposition occurring upon recycling, and various problems according to aging occurring upon long-term storage.
2. Background of the Related Art
Generally, a heat-shrinkable film is used for the covering, binding or casing of vessels, plastic bottles, glass bottles, and various rod-shaped molded parts, such as pipes, rods and woods, and particularly, used to cover a cap, body and shoulder, etc. of such articles and thus to provide labeling, protection, binding or an improvement in product value. Moreover, this is widely used for the multi-package of products, such as boxes, bottles, sheets, rods and notes, etc., and expected to find use in various applications in view of its shrinkability and shrinkage stress.
In the prior art, a heat-shrinkable film of polyvinyl chloride, polystyrene or polypropylene, etc. was covered on the vessels in a tube shape, multi-packaged and thermally shrunk. However, such a heat-shrinkable film is disadvantageous in that it has insufficient heat resistance, chemical resistance and weather resistance and thus tends to melt or tear upon boiling or retort treatment.
Particularly, the heat-shrinkable film of polyvinyl chloride produces dioxins upon incineration to cause an environmental problem. The heat-shrinkable film of polystyrene has high natural shrinkage (%) and thus the problem of a change in its dimension after storage and printing. For this reason, a heat-shrinkable polyester film has been highlighted.
In the prior art regarding the heat-shrinkable polyester film, Korean patent laid-open publication No. 2001-11259 discloses a method of producing a co-polyester film by blending polyethylene terephthalate, polytrimethylene terephthalate and neopentyl glycol co-polyester. However, this heat-shrinkable polyester film has several problems as follows. First, if the neopentyl glycol co-polyester contains neopentyl glycol at an amount larger than 25 mol %, this will be difficult to be pre-crystallized. The second problem is that this heat-shrinkable polyester film is thermally decomposed upon its recycling to cause a process problem, since it has a far lower melting temperature than the polyethylene terephthalate film. The third problem is that this heat-shrinkable film is aged upon long-term storage, since it has non-crystallinity unlike a heat-shrinkable polyester film of the present invention.